Floating tank assembling method

ABSTRACT

A method for assembling a tank is disclosed in which the uppermost side plate or shell and a roof are assembled on a bottom placed upon a foundation to form the uppermost shell assembly and an air-tight sealing mechanism is disposed within the uppermost shell assembly. The compressed air is introduced into the shell assembly so as to float the same to a predetermined height, and the segments or blocks of the next side plate are placed below the floated uppermost side plate and welded thereto. The above steps are cycled until the lowermost side plate is assembled and the assembly of the tank is completed.

United States Patent [1 1 Fujiwara et al.

[451 Sept. 23, 1975 1 FLOATING TANK ASSEMBLING METHOD [73] Assignee: Ishikawajima-Harima ,Iukogyo Kabushiki Kaisha, Tokyo, Japan 22 Filed: June 27,1973

2| Appl. No.: 374,262

[30] Foreign Application Priority Data June 28, 1972 Japan 1. 4764781 July 25, 1972 Japan A l i A 47 /3878 Dec. 8, 1972 Japan 47-123109 Jan. 17, 1973 Japan 48-7082 [52] US. Cl. r. 52/747; 52/745; 52/126; 220/5 A; 29/429 [51] Int. Cl. E04G 21/00 [58] Field of Search 29/429; 52/741, 745, 2, 52/747, 126; 220/5 A, 5 R

[56] References Cited UNITED STATES PATENTS 2,554,768 5/1951 Allen 1. 29/431 2,826,157 3/1958 Vartia 52/745 3,057,054 10/1962 Barnes 29/429 3,106,772 10/1963 Holcombe 1. 29/429 3,211,427 10/1965 Bristow 29/429 3,304,664 2/1967 Duquetteu. .1 52/2 3,436,196 4/1969 Wiggins 52/2 FOREIGN PATENTS OR APPLICATIONS 1,516,153 1/1968 France 52/745 732,797 4/1966 Canada. 29/429 703,557 4/1966 Italy t 52/745 92,621 8/1958 Norway 52/745 Primary Examiner-C, W, Lanham Assistant Examt'nerDan C. Crane Attorney, Agent, or Firm-Scrivener Parker Scrivener & Clarke [57] ABSTRACT A method for assembling a tank is disclosed in which the uppermost side plate or shell and a roof are assembled on a bottom placed upon a foundation to form the uppermost shell assembly and an air-tight sealing mechanism is disposed within the uppermost shell assembly. The compressed air is introduced into the shell assembly so as to float the same to a predetermined height, and the segments or blocks of the next side plate are placed below the floated uppermost side plate and welded thereto. The above steps are cycled until the lowermost side plate is assembled and the assembly of the tank is completed.

1 Claim, 26 Drawing Figures US Patent Sept. 23,1975 Sheet 1 of 8 3,906,700

US Patent Sept. 23,1975 Sheet 2 of8 3,906,700

US Patent Sept. 23,1975 Sheet 3 of8 3,906,700

US Patent sfipt. 23,1975 Sheet4 of8 3,906,700

US Patent Sept. 23,1975 Sheet 5 of 8 3,906,700

US Patent Sept. 23,1975 Sheet 6 of8 3,906,700

US Patent Sept. 23,1975

Sheet 7 of 8 US Patent Sept. 23,1975 Sheet 8 of 8 3,906,700

FLOATING TANK ASSEMBLING METHOD The present invention relates to generally a method for assembling storage tanks and more particularly a method for assembling storage tanks by assembling and welding a lower shell structural member or side plate to an upper shell structual member or side plate while an assembled tank structure is floated under the pressure of compressed air.

The capacity of the petroleum storage tanks is recently much increased as huge apparatus and installations are used in the petrochemist industry so that there arise the problem of increase in cost due to the increased costs of the large-sized apparatus such as cranes. scaffoldings and so on and the problem of safeguarding the working conditions for the workers working at elevated positions.

When a floating roof tank is generally constructed by the prior art method shown in FIG. 1, a bottom b is assembled over the ground on foundation a, and then side plates or shells c are assembled and welded one by one from the lowermost side plate c, to the uppermost side plate c',,. The assembled storage tank is provided with a floating roof (1 and a wind girder 2. When the tank is assembled by this method the working position becomes higher and higher so that the high scaffoldings and cranes must be used in order to provide the working platforms and to lift the shell structural members. The height of the crane used for lifting the shell structural members or side plates is increased in proportion to the height of a storage tank to be assembled, and the works at elevated positions become more dangerous. Therefore the efficiency is reduced; the construction cost is increased; and a number of assembly steps is increased. In order to overcome these problems there has been proposed a method wherein the side plate or shell of a storage tank is assembled from the uppermost side plate or shell structure, and the assembled tank structure is lifted by hydraulic jacks to a predetermined height which is substantially equal to that of the next side plate or shell structure to be joined. The next side plate is placed below and welded to the upper side plate. This method may eliminate the works at elevated positions, but there is a distinct defect that the assembled tank structure tends to be inclined or collapsed in the worst case unless the load of the assembled tank structure is uniformly supported by the hydraulic jacks. To overcome this defect there has been proposed a centralized hydraulic control system for controlling the hydraulic pressures in the jacks so that the assembled tank structure may be lifted and held in upright position in a stable manner. But as the height of the assembled tank structure is increased, it becomes extremely diffieult to stabilize or hold the assembled tank structure upright even though the centralized control system is operated in an ideal manner. Furthermore the cost of the hydraulic system for lifting the assembled tank structure is generally in excess of the cost of a crane.

A double-shell storage tank is generally constructed by the prior art method shown in FIG. 2. Inner and outer side plates or shells fand g are first assembled and then peripheral members It and i of the inner and outer roofs are welded to the top of the side plates in the form of a ring. respectively. The inner roof k is assembled in the assembled tank shell structure upon supports j erected upon the bottom b and an outer roof m is also assembled on supports 1 erected upon the inner roof k. Sealing members q are attached to the inner roof k in order to provide the air-tightness between the periphery of the inner roof k and the inner side plate f Thereafter the compressed air is introduced by a blower or compressor 0 into a chember n to be referred to as a shell assembly hereinafter, defined by the bottom b, the inner side shell fand the inner roof k so that both of the inner and outer roofs k and m are floated to predetermined heights k' and m respectively, and welded to the peripheral members It and 1'. However the welding ofthe roofs to the side walls or inner and outer shell structures must be made at the elevated positions so that the high crane must be used, the works are dangerous, the working efficiency is reduced and the cost is increased.

There has been therefore a strong demand for an improved tank construction method which may use smallsized apparatus for assemblying the tanks, reduce the cost and improve the safety and efficiency in assembly.

One of the objects of the present invention is therefore to provide a floating tank assembling method which may eliminate the works at elevated positions and facilitate the assembly of huge tanks.

The present invention will become more apparent from the following description of the preferred embodiments thereof taken in conjunction with the accompanying drawing in which:

FIGS. 1 and 2 are views used for the explanation of the prior art methods for assembling the storage tanks;

FIGS. 3-7 are views illustrating the steps of a first embodiment of the floating tank construction method in accordance with the present invention.

FIGS. 8-14 are views used for the explanation of a second embodiment of the floating tank construction method in accordance with the present invention;

FIG. 8 is a sectional view illustrating the setup for starting the assembly of a tank;

FIG. 9 is a view illustrating the tank being assembled;

FIG. 10 is a top view illustrating a temporary roof;

FIG. 11 is a sectional view thereof;

FIG. 12 is a top view illustrating a variation of a temporary roof;

FIG. 13 is a view illustrating a temporary roof provided with a discharge opening for draining rain water;

FIG. 14 is a view illustrating a temporary roof provided with a water draining opening and an air ventilation device;

FIGS. [5-19 are views used for the explanation of a third embodiment of the floating tank construction method in accordance with the present invention;

FIG. 15 is a view illustrating the setup for starting the assembly of a tank;

FIG. 16 is a sectional view illustrating a tank being assembled;

FIG. 17 is a top view of a balancing device;

FIG. 18 is a fragmentary perspective view of sealing members and a side plate for supporting the sealing members;

FIG. 19 is a fragmentary view illustrating in detail the joint between a wire rope of the balancing device and an arm;

FIG. 20-24 are views used for the explanation of a fourth embodiment in accordance with the present invention of assembling a double-shell tank;

FIG. 25 is a side view of a falling-off preventive device; and

FIG. 26 is a perspective view of a tank constructed by the method of the present invention.

First embodiment, FIGS. 3-7

Upon the foundation 1 is assembled a circular bottom 2 upon which are erected sealing side plates 3 in the form of a ring. An uppermost side plate 50 is assembled around the sealing side plates 3 in closely spaced apart relation therewith and a permanent roof 4 is assembled upon erection columns 6 and the upppermost side plate a. The roof 4 and the uppermost side plate 5a are utilized by welding thereby forming a first shell assembly. (See FIG. 3)

Sealing members 7 made of rubber are attached to the upper edges of the sealing side plates 3, and an erection floor 8 with the same height with that of the bottom 2 is assembled around the bottom 2. (See FIG. 4)

Next, balancing devices such as wire ropes 9 and winches 10 are installed so that the roof 4 is held upright in a stable manner when the first shell assembly comprising the roof 4 and the side plates 5a is floated in a manner to be described in more detail hereinafter. In the instant embodiment the roof 4 is guyed by the wire ropes 9. Thereafter the segments of the second side plate 5b which is to be joined to the uppermost side plates 50, are placed on the floor 8 around the uppermost side plate 50 in spaced apart relation therewith as shown in FIG. 5.

Next the leading end of a duct 12 extending from a blower ll is connected to a hole formed through the bottom 2 so that the compressed air is forced into the first shell assembly to float the same. When the first shell assembly is floated to a height substantially equal to that of the next side plate 5b, the segments thereof are placed below the upper side plating 5a and securely held in position by means of jigs. Thereafter the pressure in the first shell assembly is gradually reduced so that the shell assembly is rested upon the second side plate 5b. (See FIGS. 6 and 7) In the step shown in FIG. 7 the segments of the second upper side plate 5b are joined together by welding, and the horizontal seam between the uppermost side plating 5a and the second side plate 5b is welded by an automatic horizontal welding machine 13. If the seam must be welded from both sides, a welding machine l4 installed within the first shell assembly may be 'used. (See FIG. 7) Thus the second shell assembly is constructed. While the second side plate 5b is welded to the uppermost side plating 5a, the segments of a third side plate 5c are placed around the second shell assembly.

The above assembly steps for jointing the second side plate 5b are cycled so that the third side plate 5c may be joined to the second side plate 5b and a third shell assembly may be constructed. In a manner substantially similar to that described above a desired number of side plates may be sequentially assembled.

However when the lowermost side plate is joined, an opening must be provided therethrough so that the welding machine 14, the sealing side plates 13, the sealing members 7 and so on may be removed from the inside of the tank. When the lowermost side plate is welded to the bottom 2, the tank assembly is completed.

In the first embodiment, each of the side plates has been described as being placed outwardly of the sealing side plates 3, but it will be understood that it may be placed inwardly of the sealing side plates 3. Furthermore in the first embodiment the assembly of the single shell tank with the dome roof has been described, but it is to be understood that the method of the first embodiment may be also applied to the assembly of a cone roof tank or floating roof tank.

Second embodiment, FIGS. 8-14 The second embodiment of the present invention to be described in detail hereinafter with reference to FIGS. 8-14 is substantially similar to the first embodiment described above with reference to FIGS. 3-7 except that instead of the permanent roof 4 a temporary or erection roof 15 is used.

In the first step shown in FIG. 8 the uppermost side plate 5a including top angles 16 and stiffeners 17 is assembled on the bottom 2, and the sealing side plates 3 with the sealing members 7 are assembled upon the bottom 2 in a manner substantially similar to that described with reference to FIGS. 3-7. The sealing members 7 serve to provide the air-tightness between the sealing side plates 3 and the subassembled uppermost side plate 5a. Thereafter the deformable dome-shaped roof 15 made of rubber or the like is removable and airtightly mounted upon the uppermost side plate 5a, and the segments of the next side plate 5b which is to be joined to the uppermost side plate 5a are placed upon the floor 8 around the uppermost side plate 50. Thus the setup for the tank construction is completed as shown in FIG. 8. The temporary roof 15 is depending due to its own weight.

The compressed air is forced by the blower 11 into a chamber or first shell assembly defined by the bottom 2, the sealing side plates 3, the sealing members 7, the uppermost side plate 50 and the temporary roof 15 so that the roof 15 is gradually expanding upwardly into the form of a dome as shown in FIG. 9. As the air in the first shell assembly is increased in excess of a pressure W/S where W weight of the roof l5 and the uppermost side plate 5a and S the sectional area of the tank, the first shell assembly comprising the roof l5 and the side plate 50 is gradually floated upto a height substantially equal to that of the next side plate 5b as shown in F IG. 9. Thereafter the segments of the second side plate 5b are moved and placed below the uppermost side plate 50 and welded together in a manner substantially similar to that described in connection with the first embodiment. The above assembly steps may be cycled so that the side plates may be joined sequentially. After the lowermost side plate is welded to the bottom 2, the temporary roof 15, the sealing side plates 3 and the sealing members 7 are all removed from the tank and the assembly of the tank is completed.

In the second embodiment, since the temporary roof [5 must be removed after the completion of the tank, it must be simple in construction, light in weight and easy in handling so that it may be mounted and removed in a simple manner. It is therefore preferable that the temporary roof 15 is made of a tent, canvas, vinyl sheet, rubber sheet or the like so that the roof 15 may be freely deformed. It is not necessarily required that the temporary roof 15 be made of vinyl or rubber which may provide the complete air-tightness, but a cloth roof may be also used when the compressed air forced into the shell assembly is larger in quantity than the air leaking through the mesh of the cloth roof. The temporary roof 15 may have a strength only sufficient to withstand the inner air pressure so that the most economical construction of the temporary roof 15 is of course in the form of a dome or semisphere.

Next the construction of the temporary roof 15 will be described in detail with reference to FIGS. -14. In the temporary roof shown in FIGS. 10 and 11 ropes 18 are extended over the uppermost side plate 50 like ribs of an umbrella, and a cloth sheet 19 is overlaid over the ropes 18 in the form ofa dome, so that the satisfactory strength and safety may be attained.

The temporary roof 15 shown in FIG. 12 comprises a net in the form of a dome as a frame. This construction has an advantage that even when the roof is damaged so that an opening is formed, the opening will be prevented from being increased in diameter or enlarged.

The temporary roofs 15 shown in FIGS. 13 and 14 are adapted to drain the rain water from the depending roof and to ventilate the tank during its assembly. The temporary roof 15 shown in FIG. 13 is provided with a drain opening 21 at the center thereof. When the blower 11 with a sufficiently great capacity is used the shell assembly may be floated even when the drain opening 21 is not closed. The temporary roof 15 shown in FIG. 14 is provided with a center opening larger than the drain opening 21 of the temporary roof 15 shown in FIG. 13. The center opening is used not only for draining the rain water but also for ventilating the tank. The center opening is provided with a cover 22 fixed to the inner surface of the temporary roof 15 with a hinge 23, and one end of rope 24 is fixed to the upper surface of the cover 22 so that the latter may be opened or closed by pulling or releasing the rope 24 extending through the center opening and over the temporary roof to the ground or floor 8. It is not required to lock the cover 22 in the closed position with the use of bolts and nuts, but it suffices only to have the cover made into contact with the inner surface of the roof 15 in order to provide the air-tightness.

Third embodiment, FIGS. 15-19 The third embodiment to be described in detail with reference to FIGS. 15--19 as being applied to the assembly of a single-shell dome roof tank is substantially similar to the first embodiment described with reference to FIGS. 3-7 except that a balancing device 25 is used in order to hold upright the first shell assembly when the latter is floated.

The first shell assembly comprising the roof4 and the uppermost side plate 5a is assembled on the bottom 2, and the space between the sealing side plates 3 and the uppermost side plate 5a is air-tightly sealed with sealing members 26 (See FIG. 18). Thereafter the segments of the second side plate 5b which is to be joined to the uppermost side plate 5a are placed around the uppermost side plate 5a and upon the floor 8. A pair of posts 27 are erected on the bottom 2 in diametrically opposed relation inside the sealing side plates 3, and pulleys 28a, 28b and 280 are attached to the top and at the positions closer to the lower end of the post 27. An endless wire rope 29 which is wrapped around these pulleys 28a. 28b and 280 is securely fixed to an am 30 which in turn is fixed the the inner surface of the uppermost side plate 50. Thus the balancing device generally indicated by 25 is assembled. (See FIGS. 15 and 17) The number of balancing devices 25 to be used is dependent upon the capacity of the tank to be assembled, but it is preferable to use at least two balancing devices 25 in order to hold upright the uppermost side plate 5a when the first shell assembly is floated.

When the compressed air is forced into the shell assembly by the blower 11, the shell assembly is floated in a manner substantially similar to that described hereinbefore and the uppermost side plate 5a can be securely held upright by the balancing devices 25. When the shell assembly is floated to a predetermined height, the segments of the second side plate 5b are moved and placed below the uppermost side plate 5a and welded together in a manner substantially similar to that described hereinbefore. (See FIG. 16)

The welding of the seams from the inside of the tank may be effected by removing the sealing members 26 from the inner surface of the uppermost side plate 50. After the welding operation, the connection of the second side plate 5b is completed with the inspection necessary for welding. And the sealing members 26 are brought into close contact with the inner surface of the assembled second side plate 5b, and at the same time the arms 30 secured to the uppermost side plate 5a are disconnected from the endless wire rope 29; thus said arms 30 are relocated from the position of the solid line down to position of the imaginary line (dotted line) as shown in FIG. 16, so that said arms 30 are connected to the wire rope. In order to facilitate the connection, the wire rope 29 may be fixed to the arms 30 with clips as shown in FIG. 19. After the side plate is raised by one step in this manner, the arms 30 are relocated to the position of the imaginary line (dotted line); then the side plate is raised by one step again, followed by the repetition of the same process. The assembled side plates and 519 may be also held upright by the balancing devices 25 in a stable manner when they are floated again for assembly of the third side plate 56. In like manner, any desired number of side plates 5c, 5d and so on may be assembled.

Fourth embodiment, FIGS. 20-24 The fourth embodiment of the present invention is applied to the assembly of a double-shell tank as will be described in detail hereinafter with reference to FIGS. 20-24, and is substantially similar to the first, second and third embodiments.

In the step shown in FIG. 20 the uppermost inner and outer side plates 32a and 330 are assembled upon the foundation 1, and an inner roof 4a and an outer roof 4b are mounted upon the uppermost side plates 32a and 33a, respectively. A plurality of arms 35 each having a guide roller 34 rotatably fixed to the free end thereof are fixed to the outer surface of the uppermost inner side plates 32a close to the upper end thereof in equiangularly spaced apart relation in such a manner that the guide rollers 34 may be made in contact with the inner surface of the outer uppermost side plated 33a. The sealing members 7 are attached to the outer surface of the inner uppermost side plate 32a along the whole periphery therof so that the space between the inner and outer side plates 32a and 330 may be airtightly sealed by the sealing members 7. The segments of the second and third inner side plates 32b and 326 are placed on the foundation 1 around the uppermost inner side plate 32a, and the segments of the second and third outer side plates 33b and 33c are placed upon the floor 8 around the uppermost outer side plate 330.

Next as shown in FIG. 21 a manhole 36a of the inner roof 4a is opened while a manhole 36b of the outer roof 4b is closed, and the compressed air is forced by the blower 11 into the first shell assembly as in the case of the first embodiment described hereinbcfore so that the outer side plate 330 is guided by the guide rollers 34 and floated to a predetermined height. the segments of the second outer side plate 33b are placed below the uppermost side plate 33!) and welded in a manner sub stantially similar to that described in connection with the first embodiment.

Thereafter as shown in FIG. 22 the manhole 36a is opened whereas the manhole 36b of the outer roof 4b is closed. and the compressed air is forced by the blower 11 into the first inner shell assembly comprising the roof 4a and the side plate 32a so that the inner shell assembly may be floated while being guided by the guide rollers 34 rolling over the inner surface of the outer side plate 33a. When the inner shell assembly is floated to a predetermined height, the segments of the second inner side plate 32b are placed below the uppermost side plate 32a and welded together in a manner substantially similar to that described hercinbefore.

In like manner the outer and inner shell assemblies are alternately floated. and the third side plates 32c and 331' are assembled. When the lowermost inner and outer side plates are assembled. the guide rollers 34, the arms and the scaling members 7 are removed so that the double-shell tank is completed.

In the fourth embodiment, the segments of the inner side plates are previously placed inside the inner shell assembly, but if required a part of the outer side plate may be removed so as to carry the segments of the inner side plates into the inner shell assembly. Alternatively as shown in FIGS. 23 and 24 which correspond to FIGS. 21 and 22 respectively. a block ofsegments of the inner and outer plates may be formed with supports 39 by tack welding. When the outer shell assembly is floated to predetermined height. the block of the inner and outer side plates 37b and 38b is moved below the outer shell assembly in such a manner that the outer side plate 38b is in line with the upper side plate 380. Thereafter the outer side plate 380 is lowered and the seam between the upper and lower side plates 38a and 38b is welded. The inner side plate 37b is spaced apart from the outer side 38b so that the inner side plate 37b is spaced apart from the inner side plate 370 by a small distance as shown in FIG. 23. In other words the length of the supports 39 is shorter than the space between the outer and inner shell. Next the inner side plate 37b is disconnected from the supports 39 and the inner shell assembly is floated to a predetermined height so that the inner side plate 37b may be placed below the upper inner side plate 37a. The inner shell assembly is lowcred so that the upper inner side plate 37a is in line with the lower inner side plate 37b and the seam between them is welded. The above steps may be cycled so that any desired number of inner and outer side plates may be assembled.

The tank assembled by the first. second. third or fourth embodiment of the present invention is illustrated in FIG. 26.

In the first to fourth embodiments of the present invention described above. a device for preventing the falling off of the floated tank assembly generally indicated by 40 in FIG. 25 may be used. The falling off prc vcntive device 40 generally comprises a post 41. a lever 43 pivoted to the upper portion of the post 41, and a stop 44 fixed to the post 4]. The upper end of the lever 43 is made into engagement with a stop plate 42 fixed to the inner surface of the uppermost side plate 5a so that the weight of the roof 4 and the side plate 5a may be transmitted to the lever 43 and hence to the post 41. The rotation of the lever 43 may be prevented by the stop 44. Thus the first shell assembly comprising the roof4 and the side plate may be prevented from falling off when the next side plate 5b is welded to the uppermost side plate So.

It is to be understood that the present invention is not limited to the first to fourth embodiments described in detail hereinbefore, but various modifications may be effected without departing the true spirit of the present invention. For example the balancing device 25 described with reference to FIGS. 15 and 16 may be used in the second and fourth embodiments. and instead of the permanent roof, a temporary roof 15 of the type described with reference to FIGS. 8 and 9 may be used in the fourth embodiment described with reference to FIGS. 20 24.

The advantages of the floating tank assembly method in accordance with the present invention may be summarized as follows:

I. Since the tank which is being assembled is floated by the air, no special large-sized apparatus is required. so that the construction cost may be remarkably reduced. Furthermore the apparatus and devices used in conjunction with the method of the present invention are simple in construction. and the inclination or collapse of the tank under construction may be prevented. Even when the power supply to the blower is interrupted, the floated tank assembly is gradually lowered so that the tank assembly work may be safeguarded.

II. The assembly works are made at the low and predetermined positions and the side plates are sequentially assembled one by one so that the assembly works are safeguarded and the assembly efficiency is remarkably increased. Furthcrmorc the control of the tank assembly work may be much facilitated.

Ill. Since the works at the elevated positions may be eliminated. the large-sized cranes and scaffoldings may be eliminated so that the installation cost may be considerably reduced. Furthermore the tank assembly method in accordance with the present invention may be used in a limited space.

IV. The quality of the weldments may be much improved because all of the welding works may be accomplished in the stable positions.

V. Since the types of the tank assembly works are simple, the rationalization and automation of the tank assembly works may be effected.

VI. Since the weight of the tank. however large it may be. per unit area is almost same. the air or gas having a relatively low pressure may be used for floating the tank assembly so that the power cost may be minimized.

What is claimed is:

1. In an assembly of a double-shell tank, a floating tank assembling method comprising the steps of a. forming uppermost inner and uppermost outer shell assemblies by assembling on the ground inner and outer roofs and first inner and outer side plates respectively.

b. providing air-tight sealing between said uppermost inner and outer shell assemblies.

c. introducing compressed air into the uppermost inner and outer shell assemblies so as to float the 9 l uppermost outer shell assembly to it predetermined f welding a second inner side plate to the first inner B side plate of the floated uppermost inner shell asd. welding 11 second outer side plate to the first outer scmbly and side plute of the floated uppermust outer shell as g. repeating steps (0), (d)- (c) and (f) until the lowermost inner and outer side plates are welded to the inner and outer shell assemblies, respectively.

semhly.

e. intrudueing compressed air into the uppermost inner shell assembly so as to float the lustnumed assembly to a predetermined height 

1. In an assembly of a double-shell tank, a floating tank assembling method comprising the steps of a. forming uppermost inner and uppermost outer shell assemblies by assembling on the ground inner and outer roofs and first inner and outer side plates respectively, b. providing air-tight sealing between said uppermost inner and outer shell assemblies, c. introducing compressed air into the uppermost inner and outer shell assemblies so as to float the uppermost outer shell assembly to a predetermined height, d. welding a second outer side plate to the first outer side plate of the floated uppermost outer shell assembly, e. introducing compressed air into the uppermost inner shell assembly so as to float the last-named assembly to a predetermined height, f. welding a second inner side plate to the first inner side plate of the floated uppermost inner shell assembly, and g. repeating steps (c), (d), (e) and (f) until the lowermost inner and outer side plates are welded to the inner and outer shell assemblies, respectively. 